How is the due date calculated?

Using Naegele's rule: take the first day of your last menstrual period, add 1 year, subtract 3 months, and add 7 days — which equals LMP + 280 days. If your cycle is longer or shorter than 28 days, the formula is adjusted proportionally.

How accurate is the estimated due date?

Only about 5% of babies are born on their exact due date. Most are born within ±2 weeks. A first-trimester ultrasound is more accurate than LMP alone, especially if your cycles are irregular.

What does gestational age mean?

Gestational age counts from the first day of your LMP — not from conception. So at "4 weeks pregnant," you conceived approximately 2 weeks earlier. This is standard medical convention.

When do trimesters begin and end?

First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28–40. This calculator uses these standard boundaries.

Pregnancy Due Date Calculator

Quick answer: Enter the first day of your last menstrual period (LMP) to instantly see your estimated due date, gestational age, trimester, and estimated conception date.

Your estimated due date (EDD) is calculated using Naegele's rule — the same method used by OB-GYNs and midwives worldwide: add 280 days (40 weeks) to the first day of your last menstrual period. This calculator also adjusts for cycle lengths other than 28 days and tells you your current gestational age and trimester.

Last reviewed: April 2026Report an error

First Day of Last Period (LMP)

Average Cycle Length (days)

Estimated Due Date

January 12, 2027

Your estimated due date is January 12, 2027. You are currently 6 weeks and 0 days pregnant (Trimester 1). 238 days remaining.

Gestational Age

6w 0d

Trimester

1st Trimester

Days Remaining

238 days

Est. Conception

April 21, 2026

How to Use This Due Date Calculator

1Enter the date of the first day of your last menstrual period (LMP).
2Adjust cycle length if it differs from 28 days.
3Read your estimated due date (EDD) — this is 40 weeks from LMP.
4See your current gestational age in weeks and days.
5Confirm or refine with an ultrasound (first trimester ultrasound is most accurate).

Frequently Asked Questions

: Using Naegele's rule: take the first day of your last menstrual period, add 1 year, subtract 3 months, and add 7 days — which equals LMP + 280 days. If your cycle is longer or shorter than 28 days, the formula is adjusted proportionally.
: Only about 5% of babies are born on their exact due date. Most are born within ±2 weeks. A first-trimester ultrasound is more accurate than LMP alone, especially if your cycles are irregular.
: Gestational age counts from the first day of your LMP — not from conception. So at "4 weeks pregnant," you conceived approximately 2 weeks earlier. This is standard medical convention.
: First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28–40. This calculator uses these standard boundaries.

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Pregnancy Due Date Calculator

How to Use This Due Date Calculator

Frequently Asked Questions

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